In electrostatic printers, a sheet having a photoconductive layer is given an electrostatic positive or negative charge in the dark, such as by means of a corona-charging device. The charge layer is then exposed to a light image of an original document to cause the charge on the layer to leak off in non-image areas and selectively leave a latent electrostatic charge image. This latent image is then developed by applying to the photoconductive layer a toner containing particles which have a charge opposite to the residual electrostatic charge image so that the toner particles adhere to the charged areas and form an image. In order to function properly for this purpose, the toner must be capable of producing a colored layer of suitable density on the charged areas without unduly coloring the uncharged or background areas. Although there are many liquid toners which serve satisfactorily in the electrophotographic production of copies, each generally has a drawback, such as bad effect on the background, low stability and poor ability to produce sharp black copies at a reasonable cost.